Heat dissipation unit with direct contact heat pipe

ABSTRACT

A heat sink for integrated circuits is limited substantially to heat transfer fins on one or more heat pipe tubes, the tube(s) functioning as a base for the heat sink. The heat pipe tube has a flattened oval cross section and can snap-fit in openings through the fins. The tube is exposed on one side of the heat sink for contact with the heat generating circuit. The fins can be flat or irregular and can have a collar engaging the heat pipe tube. In one example, the heat pipe tube runs perpendicular to vertical fins along the bottom of a standing fin stack. In another embodiment two U-shaped heat pipe tubes carry a layered stack, the bottom of the U-shapes being presented under the lowermost in the stack. A clamp urges the heat sink against the heat source.

FIELD OF THE INVENTION

The invention relates to heat exchangers, and in particular to a unitfor dissipation of heat from a processor or other integrated circuit.One or more heat pipe tubes for thermally conductive contact with thecircuit package extends along an edge of an array of parallel airconvection fins. The heat pipe tube(s) are tapered toward a plane ofcontact with the circuit package, preferably having a flattened ovalcross section. This maximizes contact surface area on the heat pipetubes and also provides a shape that structurally engages and supportsthe parallel fins on the heat pipe tubes. A clamping fixture arranged inthe array of fins provides another structural member and a point forapplication of force to urge the heat pipe tubes into conductive contactwith the circuit package.

BACKGROUND OF THE INVENTION

Various electrical semiconductor devices, such as large scale integratedcircuits, voltage regulators, current switching devices, high speed orhigh current circuits and other similar devices, generate heat that canbe deleterious to their own operation and must be dissipated. If theambient air adjacent to the circuit is at a lower temperature than thecircuit device, some heat energy is dissipated by heating of the ambientair. The relatively hot circuit device heats the relatively cooler airthat comes into contact with the circuit device. The heated air iscirculated by convection and replaced by cooler air, thus moving heatenergy away from its source.

The rate of heat energy transfer frequently must be sufficient to keepthe heat source below some specified limiting temperature. A number oftechniques are used to facilitate movement and dissipation of thermalenergy from a heat source. Some techniques rely on the nature of theheat sink, which could comprise a solid, liquid or gaseous medium. Othertechniques rely on unique structural attributes. It is possible to usedifferent mediums together. It is possible to vary the structuralattributes to meet various objectives. Such objectives include the heattransfer rate, the thermal inertia of the sink, its size and weight,manufacturing and material costs, etc.

For dissipation of heat energy into the air, for example, maximizing thesurface area of air contact is a consideration, often leading to heatsink structures with thin metal plates or fins for thermal conduction.Consideration also must be given to how the heat is coupled into thefins, often leading to solid metal base plate blocks for contact withthe heat source, the base plate block being cast integrally with fins.Structures can be provided to engage with the base plate block, such asclamps or springs and for mounting of a supplemental fan to force airover the fins.

One technique for moving heat energy, which technique is very apt forcompact or portable devices having digital processors or the like thatgenerate substantial resistive heating, is to employ a heat pipeconfiguration to move heat energy from point to point. In a heat pipearrangement, a captive heat transfer fluid typically is provided inclosed thermally conductive envelope. The fluid circulates in a mannerwhereby heat is taken up at a point that is in thermal contact with theheat source, and the heat is released at a point in thermal contact witha heat sink.

The thermal path advantageously employs a cycle of phase changes of theheat transfer medium. The heat transfer medium is brought in a liquidphase to an evaporator. Heat from the circuit or other heat source boilsor vaporizes the heat transfer medium at the evaporator. The resultinggaseous phase diffuses through the envelope and encounters a condenserassociated with a heat sink. At the condenser, the gaseous phase iscooled and condenses back to a liquid. A return flow path re-circulatesthe condensed liquid phase back to the evaporator, closing the loop. Ina heat pipe, capillary flow through a wicking material can provide thereturn flow path. The typical return flow path in the case of athermo-siphon is gravity driven. Each phase change stores or releases aquantity of heat energy due to the latent thermal energy involved in thephase change itself.

Phase change heat exchange circuits as described can operate with a verymodest temperature difference between the source (evaporator) and thesink (condenser) while moving heat energy. Nevertheless, it is a typicalattribute of most heat pipe designs that a discrete area of theconductive envelope functions as the evaporator, and a different areathat is more or less remote from the evaporator functions as thecondenser. If the structure of the envelope is thermally conductive andthe condenser part is very close to the evaporator part, then heatenergy coupled into the envelope at the evaporator tends to heat thecondenser by conduction through the material of the envelope.

The ultimate object of a heat dissipation structure is to couple heatenergy from the area of the evaporator to that of the condenser. The useof a heat pipe with a phase change medium has the further object ofmaintaining the evaporator and condenser respectively above and belowthe vaporization temperature of the medium. In U.S. Pat. No.6,1,63,073—Patel, an integrated heat sink and heat pipe are provided.The heat sink has a cast base plate and vertically extending fins, thefins being cast integrally with thee base plate. The base plate has oneor more elongated openings that extend along the bottom of the baseplate, and either open downwardly toward the heat source or are justbarely placed below the surface so as to minimize material between theopening and the heat source. Elongated heat pipes are disposed in theelongated openings, which: are exclusively within the thickness of thebase plate.

The '073 Patel patent explains that the area of the heat sink is muchgreater than the area of the heat source. This might suggest that thearea in direct contact with the heat source functions as the evaporator,and areas that are remote from the heat source function as condensers.The patent teaches that this structure reduces thermal, gradients in theheat sink. If in an ideal case there is no thermal gradient across theheat sink, then at that area in contact with the heat source, thetemperature of the heat sink would be as low as possible, providing goodcoupling of thermal energy into the heat sink. That ideal case, however,presumably would not rely on a phase change between an evaporator and acondenser.

The Patel patent teaches alternative structures for the heat pipes thatare placed along the side of the base plate that is to contact the heatsource. In the embodiments wherein the openings on the underside of thebaseplate are channels opening at the surface, the heat pipes can beD-shaped rather than round in cross section, with the flat side facingthe heat source. The channels are complementary, with U-shaped crosssections, providing for full surface contact.

In a different sort of finned heat pipe arrangement, for example asshown in U.S. Pat. No. 5,329,993—Ettehedieh, the base plate part of afinned structure carries an array of passage:s that function as anevaporator, and these passages are coupled to standing hollow columnsthat are coupled to the passages in the base plate and function ascondensers. An array of parallel (horizontal) fins is coupled to thestanding (vertical) columns. This arrangement has structural advantages,but is complex.

It would be advantageous if thermal efficiency, mechanical complexityand production ease: could be maximized in a finned heat pipearrangement that is at the same time compact and inexpensive.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a heat sink that does notrely on a base plate block to contribute to the structural or thermalattributes of the heat sink.

It is an object to structure the cross sectional shape of a heat pipe soas to structurally engage complementary openings in a plurality of finsin a stack.

It is a further object to provide reinforced openings in heat exchangefins, which openings are easily manufactured, for fixing the relativepositions of heat sink parts.

It is another object to adapt a heat pipe structure such that the finsand/or the heat pipe elements carry all necessary mounting hardware andprovide a rigid and lightweight structure that is substantially entirelyoptimized for heat transfer functions.

These and other objects are accomplished by a heat sink for integratedcircuits, which is limited substantially to a stack of heat transferfins on a heat pipe tube. The heat pipe tube has a flattened oval crosssection and fits a complementary opening through the fins. A channel canbe formed by aligned openings at the edge of the fins, exposing the heatpipe for direct contact with the heat generating circuit. The finssnap-fit with the tube and can have a collar to space the fins and/orextend the surface area of engagement. The air contact areas of the finscan be flat, or can comprise continuous folded or rolled form materialwherein the variation from a flat shape provides greater total surfacearea per unit of outside dimensions (e.g., per unit of footprint area).

According to one aspect, the heat pipe can be snap fit in a channelrunning perpendicular to vertically oriented fins, along the bottom ofthe stack. In another embodiment, the upward legs of two U-shaped heatpipe tubes carry the stack. In that case, the bottoms of the U-shapedtubes are presented for contact with the circuit, under a stack ofhorizontal fins. A clamp urges the heat sink against the heat source.

The structure is inexpensively built from the minimum necessary partsand provides advantages including compact size, light weight, goodthermal efficiency, low thermal inertia and low cost.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will bemore fully disclosed in, or rendered obvious by, the following detaileddescription of the preferred embodiments of the invention, which are tobe considered together with the accompanying drawings wherein likenumbers refer to like parts and further wherein:

FIG. 1 is a perspective view of a heat dissipation unit with directcontact heat pipe according to the invention, the bottom part in theorientation shown being the side to be directed against a circuit deviceto be cooled.

FIG. 2 is a partial perspective view showing a detail of the finstructure at one of the openings that are aligned in FIG. 1 to form achannel for a heat pipe tube.

FIG. 3 is a partial perspective view illustrating the relationship ofthe heat source, heat pipe and fins of the heat dissipation unit.

FIG. 4 is a perspective illustration showing an alternative embodimentwherein the section of the heat pipe arranged for direct contact withthe heat source is a flat segment at the bottom of a squared U-shapeconfiguration of one form of dual heat pipe for use with the invention.

FIG. 5 is an elevation view showing mounting of the heat dissipationunit of FIG. 4 using spring clips.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This description of preferred embodiments is to be read in connectionwith the accompanying drawings, together forming the description of theinvention and illustrating certain nonlimiting examples. The drawingfigures are not necessarily to scale and represent some features inschematic form, in the interest of clarity and conciseness.

The invention provides a heat transfer device 32 for dissipating heatdeveloped by a source such as an integrated circuit package. The devicetakes up heat energy by conduction with the source, and dissipates theheat by convection and radiant cooling, into the surrounding air. It isan aspect of the invention that the thermal energy pathways are asdirect as practicable, and the structure of the device is substantiallylimited to those elements that are directly related to engaging the heattransfer device with the source and to dissipating the heat that thedevice collects.

An exemplary embodiment of the heat transfer device is shown in FIG. 1.A plurality of fins 35, spaced from one another and arranged in a stack38, are provided for heat exchange with the ambient air. A heat pipestructure 40 is thermally coupled to the fins 35, and has at least onethermally conductive envelope 43. The envelope 43 contains a workingfluid for distributing heat energy.

In FIG. 1, the heat transfer device 32 is shown from below and from oneend, the point of view being based on the assumption that the heattransfer device 32 preferably is arranged to reside vertically over theheat source (not shown in FIG. 1) so as to take advantage of convectionin order to circulate the air around the heat transfer fins 35. Thisorientation is efficient in the absence of a forced air current, but isnot required to achieve many of the benefits of the invention.

Generally, any spatial and similarly relative terms used in thisdescription, whether denoting an overall orientation such as“horizontal,” “vertical,” “up,” “down,” “top” and “bottom” or theirderivatives (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) areintended to refer merely to the orientation of the item then beingdescribed and shown in the drawing under discussion. Such spatial andrelative terms are used for convenience of description and should not beconstrued to require a particular orientation in any other context. Thesame considerations apply to internally relative terms such as“inwardly” versus “outwardly,” “longitudinal” versus “lateral” and thelike, which are to be interpreted relative to one another or relative toan axis of elongation, rotation, assembly or the like, as appropriate tothe description at that point.

Terms stating or implying relationships of attachment or coupling,whether mechanical or thermal or otherwise, refer to a relationshipwherein the structures can be attached, coupled, connected (etc.)directly or indirectly through intervening structures that maycontribute to such attachment or coupling. Attachments, couplings andthe like also can be movable or rigid, continuous or intermittent, etc.,unless otherwise required according to the context of these particularterms. Where elements are “operatively” connected, attached, or coupled,that connection, attachment or coupling is intended to denote aconnection or the like that allows the pertinent structures to operateas stated, generally but not necessarily by virtue of such relationship.

Referring again to the view in FIG. 1, the embodiment shown has a heatpipe structure 40 comprising two heat pipe tubes 43 that are elongatedin a direction perpendicular to the parallel spaced planes of a numberof heat transfer fins 35. The fins 35 each comprise a rectangular thinsheet metal plate, which is formed to engage mechanically and thermallywith the heat pipe tube 43. The fins 35 are shown as flat plates in thisembodiment, but could be formed with more surface area per unit ofoutside area, for example using a continuous folded, sinusoidal orsimilarly corrugated form, or by rolling, stamping or otherwiseembossing a pattern in the plates, such as an array of bumps, ridges orthe like. Forming irregularities in the shape in this way isadvantageous for providing a high ratio of surface area to volume.Irregularities also produce local air, flow eddies. But an irregularshape has a greater resistance to air flow parallel to its surface thana smooth shape.

According to an inventive aspect, one or more thermally conductiveenvelopes or heat pipe tubes 43 of the heat pipe structure 40substantially define the mounting base for the heat transfer device 32.Thus there is little structure needed other than the fins 35, which areshaped to engage with the heat pipe tubes 43, and the heat pipe tubes 43themselves.

The heat pipe tubes or envelopes 43 are attachable to a heat source(shown in FIGS. 3 and 5) for thermal energy exchange by conduction withthe heat source through direct contact. The heat pipe tubes 43 are alsoin contact with the air contacting fins 35. Thus, any heat energycoupled into the heat pipe tubes 43 is in turn coupled into the fins 35and is dissipated into the ambient air by convection and/or forced aircooling.

In addition to coupling thermal energy to the fins 35, the heat pipetubes 43 mechanically support the fins. As shown in FIGS. 1 and 2, thefins 35 have formed openings 52 that, in this embodiment, are arrangedalong the extreme edges 54 of the fins 35. The fins 35 in the stack 38are substantially aligned, the openings 52 in successive fins 35 forminga channel 56 that is complementary with the outside shape of theconductive envelope or heat pipe tube 43.

Two heat pipe tubes 43 are shown in FIG. 1. Each of the tubes is engagedin corresponding openings 52 in the stacked fins 35, an exemplaryopening being shown in FIG. 2. The stack of fins 35 is supported inregistry by engagement with the heat pipe tube or tubes 43. The fins 35in this embodiment are formed with openings 52 in a shape that becomesat least slightly wider proceeding inwardly from the extreme edge 54 ofthe fins 35. The tubes 43 have a complementary shape. This permits thefins to be snap fitted on the heat pipe tubes 43.

The heat pipe tubes 43 present a flat face 57 outwardly (downwardly inFIG. 1) substantially along the aligned edges of the fins 35. That flatface is engaged in surface contact with the heat source (not shown inFIG. 1). It is also possible to provide an arrangement in which the heatpipe tubes or thermally conductive envelopes are not snap fitted intothe edge of the stack 38 as shown in FIG. 1, instead being insertedendwise through openings that are spaced from the edges of the fins 35.Such an embodiment is shown in FIG. 4 and is discussed below.

In FIG. 1, in order to achieve the snap fitting aspect and to presentthe flat face 57 toward the heat source, the heat pipe tubes 43 have aparticular cross sectional shape characterized by a decreasing width,proceeding toward the edge 54 of the fins 35. The openings 52 in thefins 35 also have a complementary shape, namely with a decreasing spanof the openings along the edges or the fins. As a result, when the fins35 are fitted to the tubes 43 by pressing the tubes 43 into the channels56 defined by the openings 52 in a stack of fins (or vise versa) the twosnap together. The part of the fins at the minimum span of the opening,and/or tubes at the point of increasing width, interfere and areresiliently deformed. As these interfering parts pass, they snap back totheir rest position and hold the fins and the tubes in substantiallyrigid mechanical attachment.

A preferred shape for achieving this snap fitting is the flattened ovalor lozenge shaped cross section 62 of the heat pipe tube 43, shown inFIG. 3. The tube 43 has a relatively wide and flat face 57 presentedtoward the heat source 72, namely downwardly in FIG. 3. The two lateralsides 75 of the tube are rounded and in this embodiment lead to asymmetrically flat opposite face 77 on the top side of the tube 43. Theopposite face 77 need not be flat. The lozenge or flattened oval crosssection 62 has a relatively narrower width at the tangent between theflat outer-face 57 and the curve on the lateral sides 75, and arelatively greater width at the outside peak of the rounded lateralsides 75. The openings 52 in the fins are complementary with theflattened oval 62 at least to the extent that the span between the sidesof the channel formed by openings 52 extends beyond and is narrower thanthe maximum width of the tube 43 between the peaks of the roundedlateral sides 75. That is, the openings in the fins 35 are at leastsomewhat narrower at the extreme edge 54 of the fins 35 than they are ata point spaced inwardly from the edge 54, corresponding to the peakbetween the rounded ends 75.

The foregoing structure enables the fins 35 to be snap-fitted to theheat pipe tubes 43 or vice versa. The openings 52 in the fins could becut from flat stock, i.e., with the fins 35 shaped simply as flat sheetswith voids or cutouts 52 complementary with the flattened oval heatpipes 43 opening at the edge 54. However, according to another aspect,the openings 52 at the edges of the fins 35 are formed, for example in astamping procedure, to provide a formed collar 82 in the flat sheetmaterial, raised from the plane of the sheet material around at leastpart of the opening 52 and thus encompassing a length along the channel56 for the heat pipe tube 43, which length is greater than the thicknessof the sheet material.

An exemplary formed collar 82 on a fin 35 is shown in FIG. 2. The collarcan be more or less continuous around the heat pipe tube opening, but atleast in the area of the heat source, the heat pipe tube 43 is exposedfor direct contact with the source for good thermal transfer efficiency.Therefore at least in this area the opening for the heat pipe tubecrosses over the edge of the fin.

The heat pipe tubes may be longer than the corresponding dimension ofthe heat source, causing the ends of the tubes 43 to extend beyond theend of the heat source. In that case it not necessary for the heat pipetubes to be exposed for contact and it is efficient for heat transferpurposes for the openings in the fins to be spaced back from the edge 54of the fin plate. This could involve making the fins 35 verticallyshorter where the heat pipe tubes 43 are exposed, such as at a midpointbetween the ends, and longer at the ends. The heat pipe tubes 43 alsoneed not be straight and could extend in an upward incline toward theends of the tubes (not shown). Depending on the orientation of the fins,the heat pipe tubes also can follow a right angle bend, shown in FIG. 4.

Each heat pipe 43 serves to distribute heat energy coupled to the heatpipe from the he at source, such as an integrated circuit package 72,shown in FIGS. 3 and 5. The heat source couples heat to the heat pipe 43at a relatively concentrated area that is in direct contact with thesource and functions as an evaporator. The heat pipe conductively and bythermal phase change conveys that heat energy, to the remainder of theheat pipe and distributes the heat energy to the fins 35. In a preferredarrangement, the heat pipe vessel comprises a highly thermallyconductive material, normally a metal. Silver, gold, copper, aluminum,titanium or their alloys are useful, with some tradeoff being made forthermal conductivity versus expense. Polymeric materials can also beused, including materials known in the electronics industry for heattransfer applications, such as thermoplastics (crystalline ornon-crystalline, cross-linked or non-cross-linked), thermosettingresins, elastomers or blends or composites thereof that arecharacterized by thermal conductivity.

The working thermal transfer fluid can be selected from a variety ofwell known two phase fluids depending upon expected operationalconditions such as the operating temperature range over which the heattransfer device will operate. Appropriate fluids may include, forexample, one or more of water, Freon, ammonia, acetone, methariol,ethanol and the like. The prime requirements for a suitable workingfluid are compatibility with the materials forming wick and the envelopewall, good thermal stability,lease of wetting of the wick and wallmaterials as well as viscosity and surface tension attributes suitablefor capillary flow.

Referring to FIG. 3, the thermally conductive tube 43 is provided with awicking material along its inner surfaces, such as a granular form of asimilarly thermally conductive material as compared to the material ofthe tube, bonded adhesively or sintered so as to provide a porous masswith capillary sized passages. The tube is charged with a thermalworking fluid and partially evacuated. Thermal energy transfer occursconductively through the material of the tube, but importantly, the areaof the tube that is in the most intimate contact with the heat source72, namely the flat face 57 of the flattened oval shape 63 in FIG. 3that functions as the supporting base surface of the device, reaches aslightly higher temperature than other portions of the tube 43, such asportions that are more closely coupled to the fins 35 than the heatsource 72 and/or are more remote from the concentrated heat energy atthe heat source, such as ends of the tubes 43 that may extend beyond theedges of the heat source 72.

The area 57 of the tube in contact with the heat source 72 functions asan evaporator at which the working fluid is vaporized. The working fluiddiffuses in the gaseous phase throughout the tube. At areas where theinside surfaces of the tube are slightly cooler, even by a relativelysmall temperature difference, the gaseous working fluid condenses. Inthe process of condensing, the fluid transfers the latent energy of itsvaporization to warm the heat pipe tube 43 at that slightly cooler area,which functions as a condenser. The working fluid in the liquid phaseflows back again by capillary action of the wicking material and isagain vaporized in a continuing cycle. Capillary flow in wickingmaterial provides a returning liquid phase flow path that does not relyon gravity (although gravity may contribute to the flow in certainorientations).

The overall effect is to reduce the concentration of elevatedtemperature that would otherwise be maintained at the heat source 72.The temperature at portions of the heat pipe 43 that are remote from theheat source, such as the far ends 92 of the heat pipe, is elevated. Heatenergy is moved from the source and coupled into the fins 35. The finsin turn transfer the heat energy into the surrounding air, which ismoved by convection or optional forced air circulation. This moves theheat finally away from the heat sink and away from source 72. The heatdissipation unit as described couples heat energy to the fins at leastas efficiently as a comparable heat sink that relies only on conductionfrom a base block to a similar array of fins, and normally is moreefficient due to the relative lack of concentration of heat near thesource in the heat pipe arrangement of the invention, and/or due to therelatively elevated temperature difference between remote areas on thefins and the surrounding air, compared to a simple thermal conductionfinned heat sink.

As noted above, the fins preferably are formed with collars 82 thatextend for a short distance longitudinally along the heat pipe tubes 43.The longitudinal dimension of the collar and the relative span of theopening versus the width of the heat pipe tube are subject tovariations, provided that there is sufficient clearance to snap theparts together, preferably snugly so that the assembly is substantiallyrigid as snapped together and the fins are operatively engaged inthermally conductive contact with the heat pipe tubes.

The longitudinal extension of the collars 82 increases the surface areaof contact between the heat pipe tubes and the fins, as compared to astrictly planar sheet metal fin, which is helpful for thermal transferefficiency. The longitudinal extension of the collars 82 also improvesthe rigidity of the mechanical connection of the fins 35 to the heatpipe tubes 43. Thus the heat pipe tubes 43 provide a secure base for arigid structure comprising the fins and the heat pipe tubes.

The formed collars 82 of the fin openings 52 can be axially orlongitudinally high enough to space at least certain of the fins fromthe next adjacent fin. In the embodiment shown, the collars do notextend longitudinally on the heat pipe tubes 43 all the way to the nextadjacent fin. The fins can be formed such that the collars do not allface in the same direction for end-to-end abutment of the collars. In anembodiment as shown wherein two heat pipe tubes are provided, thecollars for one tube can be oriented in the opposite direction from thecollars for the other tube, further contributing to rigidity of theassembly.

The heat pipe tubes 43 provide in one structure both the mechanical baseon which the fins are mounted in a rigid assembly, and a primary pathwayin a thermal energy transfer path from the source 72 to the fins 35. InFIGS. 1-3, the openings 52 in the fins 35 open at an outside edge 54 ofthe stack 38 and are aligned to define a channel 56 for the heat pipetube 43. As already described, the channel is characterized by areduction in channel width or span approaching the outside edge 54 ofthe associated fin 35, and an increase in width or span proceedinginboard away from the edge 54 of the fin. The shape of the opening andthe inside surface of collar 82 are at least partly complementary to theshape of the heat pipe tube 43, and preferably are substantially formfitting for maximum surface contact. Providing that the difference inwidth from the widest to the narrowest point is in the range ofresilient deformation of the tube 43 and fins 35, respectively, the heatpipe or conductive envelope is snap-fittable into the channel 56 forstructurally supporting the fins and providing a thermal contact heattransfer pathway.

The conductive envelope (heat pipe) has a flattened surface 57 facingoutwardly from the channel 56 and as shown in FIGS. 1-3, the flat faceor surface 57 is presented as the outermost surface of the heatdissipation unit, which is a rectilinear block in this example. All thatremains is to mount the heat dissipation unit with surface 57 in thermalcontact with the heat source 72. This embodiment has two discrete heatpipe tubes 43, both with an oval cross section having a flattenedsurface at least on a side facing outwardly from the channel 56. Theflat faces of the two heat pipes are coplanar as shown. They could beplaced at different levels in an embodiment having a heat source thatwas other than a flat package, or to dissipate heat from two sources atdifferent elevations relative to the stack, using the same array offins.

It is possible to provide more than the two heat pipe tubes shown. Thetubes can be relative larger width individual tubes, or more numerousrelatively smaller width tubes. Finite element heat transfer analysissoftware can be used to model the heat transfer characteristics of theunit in transient and steady state conditions, to optimize the relativesizes of the parts in view of the expected heat load, operatingtemperature differences and temperature ranges, air flow and materialthermal conductivities.

In the example, the fins 35 are substantially planar sheets but for aformed collar, raised around at least part of the channel 56. It ispossible to provide greater fin surface area in a given volume byproviding a rippled sheet configuration with folds, corrugations, rolledor embossed irregularities, etc. On the other hand, a smooth and flatconfiguration presents less resistance to air flow passing over thesurface of the fins.

An objective of the configuration shown in FIG. 1 is substantially tolimit the structure of the unit to the bare elements that are needed toprovide a unitary structure with the necessary thermal energy transfereffects, thus achieving cooling in an optimally compact, light weightand minimally expensive heat sink unit. However one necessary functionis to mount the heat sink unit in contact with the circuit package orsimilar heat source 72. FIG. 1 illustrates the attachment of a springclip and receptacle 94 to the stack 38 of fins 35. The spring receptaclein this embodiment is placed on the fin stack instead of the heat pipetubes 43 that ultimately need to be clamped against the heat source,partly because tubes 43 are relatively inaccessible under the stack 38.However this arrangement works very well, because by clamping the heatpipe tubes by force applied between the fins and the mounting for thecircuit package (not shown in FIG. 1), the rigidity of the assembly isfurther improved. The resilience of the clip in this embodiment alsopresses the fins 35 against the heat transfer pipes 43, however it ispreferable if the connection of the fins to the heat pipes is relativelyclose even without exertion of pressure. The intimacy of the connectionbetween the fins and the heat pipes can also be improved by soldering oradhesively affixing the fins and the heat pipe tubes.

Various clamping fixtures are possible. The depicted fixture is affixedto the fins 35 at a space from the conductive envelope or heat pipe 43.The clamping fixture provides a point for attachment in clamping theheat transfer device to a heat source, i.e., a mechanical mounting,while also resiliently clamping the heat pipe 43 into thermallyconductive contact with the heat source 72.

In FIGS. 1-3, the stack of fins is supported substantially exclusivelyby the conductive envelope (heat pipe tube) 43 and the clamping fixture.The heat sink or heat dissipation unit shown consists essentially of aplurality of planar fins 35 spaced from one another in a stack 38, atleast one heat pipe tube 43 extending through the stack, two beingshown, and a damping fixture 94 to be affixed between the fins and thecircuit package to be cooled. The fins 35 have aligned openings 52 thatare complementary with an outside size and shape of the heat pipe tube43, for structurally attaching the fins and the heat pipe tube. Theclamping fixture 94 can be affixed to one or the other or both of thefins 35 and the heat pipe tube(s) 43, the mounting fixture beingoperable to hold the heat sink such that the heat pipe tube is urgedagainst the flat surface of the circuit package.

FIGS. 4 and 5 show an embodiment wherein channels formed by alignedopenings in the fins are spaced inwardly from the edge of the stack andthe evaporator area along the heat pipe tubes 43 extends parallel to theplanes of the fins. The fins in this stack are oriented parallel to theplane of contact with the circuit package, rather than perpendicular tothat plane as in FIGS. 1-3. In this arrangement, the heat pipe tubes orenvelopes 112 are flattened ovals as described above, presenting a flatside 57 for contact with the circuit package. The heat pipe tubes 112(two being shown) are U-shaped, the bottom of the U-shape forming a flatbottom section 114. The flat bottom part of the U-shape also has theflattened oval or lozenge cross sectional shape as discussed, presentingtwo flat areas on the two tubes, including the flat bottom section 57wherein the heat pipe tubes form a structural base for the circuitpackage in a manner similar to that described above. In this case,clamping is accomplished by one or more separate resilient clampingfixtures 116, each having a bow part 118 that clamps over the bottomsections of the heat pipe tubes and clasps that affix to the circuitcard for holding the unit in place. As in the previous embodiment theclamping fixture engages with corresponding elements on the circuitboard 120, typically mounted to the sides of the receptacle for theprocessor unit, display driver, memory or similar circuit element to becooled.

An advantage of these embodiments of the invention is that no base plateblock is required or included. The support and thermal contact functionsof a baseplate block are met directly by the heat pipe tubes 43 or 112that also distribute and move the thermal energy away from the source.This is efficient in terms of heat transfer efficiency, is compact andlightweight, and is relatively inexpensive to manufacture.

The invention is versatile and applicable to fin or heat pipe tubearrangements of various types and oriented in various ways. Theflattened oval heat pipe tube provides a useful evaporator surface inthe area of the heat source, and also provides useful condensing andreturn flow structures elsewhere in the tube. The tube can be a straightline spine for the fins or a more complicated tower arrangement withplural U-shaped or similarly configured sections.

It is to be understood that the invention is not limited only to theparticular constructions herein disclosed and shown in the drawings, butalso encompasses modifications or equivalents within the scope of theappended claims.

What is claimed is:
 1. A heat transfer device for dissipating heat, thedevice comprising: a plurality of air heat exchange structures arrangedfor heat exchange with ambient air; a heat pipe structure comprising atleast one thermally conductive envelope containing a working fluid fordistributing heat energy wherein the heat exchange structures comprise aplurality of spaced fins formed with openings that substantially alignwith one another and are disposed alone an outside edge of the stack soas to be aligned to define a channel, wherein said channel has areduction in channel width approaching the outside shape, and whereinthe conductive envelope is snap-fittable into the channel forstructurally supporting the fins and further wherein the fins arecomplementary with an outside shape of the conductive envelope andarranged in a stack, so as to be substantially exclusively supported bythe at least one thermally conductive envelope; wherein the thermallyconductive envelope of the heat ripe structure substantially defines amounting base for the heat transfer device, the envelope of the heatpipe structure being attachable to a heat source for thermal energyexchange by conduction with the heat source, and wherein the heat pipestructure supports the heat exchange structures in thermal relation withthe conductive envelope; wherein the conductive envelope also has aflattened surface facing outwardly from the channel.
 2. The heattransfer device of claim 1, wherein the fins comprise substantiallyparallel flat sheets.
 3. The heat transfer device of claim 1, whereinthe fins comprise sheets that have an irregular shape comprising atleast one of folded, corrugated, sinusoidal, rolled, stamped andembossed shapes, including one of bumps and ridges.
 4. The heat transferdevice of claim 1, wherein the fins are snap-fittable over theconductive envelope.
 5. The heat transfer device of claim 1, wherein theconductive envelope defines an oval cross section having a flattenedsurface at least on a side facing outwardly from the channel.
 6. Theheat transfer device of claim 1, wherein the fins are substantiallyplanar sheets but for a formed collar raised around at least part of thechannel.
 7. The heat transfer device of claim 6, wherein the formedcollar of the fins spaces at least certain of the fins from a nextadjacent fin.
 8. The heat transfer device of claim 1, wherein the finshave at least two said complementary heat pipe structure comprises atleast two sets of aligned openings and at least two lengths of saidconductive envelope that are complementary with and are received inrespective ones of the sets of openings.
 9. A heat transfer device fordissipating heat, the device comprising: a plurality of air heatexchange structures arranged for heat exchange with ambient air; a heatpipe structure comprising at least one thermally conductive envelopecontaining a working fluid for distributing heat energy wherein the heatexchange structures comprise a plurality of spaced fins formed withopenings that substantially align with one another and are (i)complementary with an outside shaped of the conductive envelope and (ii)arranged in a stack, and are substantially exclusively supported by theat least one thermally conductive envelope; wherein the thermallyconductive envelope of the heat pipe structure substantially defines amounting base for the heat transfer device, the envelope of the heatpipe structure being attachable to a heat source for thermal energyexchange by conduction with the heat source, and wherein the heat pipestructure supports the heat exchange structures in thermal relation withthe conductive envelope; further comprising a clamping fixture affixedto the fins at a space from the conductive envelope, the clampingfixture providing a point for attachment in clamping the heat transferdevice to a heat source.
 10. The heat transfer device of claim 9,wherein the stack of fins is supported substantially exclusively by theconductive envelope and the clamping fixture.
 11. A heat sink for acircuit package having a flat surface presented for conductive contact,the heat sink consisting essentially of: a plurality of air heatexchange structures, shaped generally as spaced fins, forming a stack;at least one heat pipe tube extending through the stack, the fins havingaligned openings that are complementary with an outside size and shapeof the heat pipe tube, for structurally attaching the fins and the heatpipe tube wherein the heat pipe tube extends through said alignedopenings along an edge of each of said fins, the openings forming atleast one channel along a side of the stack of fins; and, a clampingfixture affixed to at least one of the fins and the heat pipe tube, theclamping fixture being operable to hold the heat sink such that the heatpipe tube is urged against the flat surface of the circuit package;wherein said at least one heat pipe tube has a flattened side facingoutwardly of the channel and the heat pipe tube has a shape with arelatively wider part disposed below an outer surface of the channel,and, wherein the channel has a relatively narrower width at a pointoutwardly in the channel from said relatively wider part, therebycapturing the heat pipe tube and the fins to one another by the shape ofthe heat pipe tube and the channel; and further wherein the fins areshaped to form a cutout at the channel and a collar extending part wayaround the heat pipe tube, the heat pipe tube being snap fit into thechannel.
 12. The heat sink according to claim 11, wherein the finscomprise one of a flat shape and an irregular shape comprising at leastone of folded, corrugated, sinusoidal, rolled, stamped and embossedshapes, including one of bumps and ridges.
 13. The heat sink accordingto claim 11, wherein the heat pipe tube has a generally oval crosssection with a flat face disposed outwardly toward the circuit package.14. A heat sink for a circuit package having a flat surface presentedfor conductive contact, the heat sink consisting essentially of: aplurality of air heat exchange structures, shaped generally as spacedfins, forming a stack; at least one heat pipe tube extending through thestack and having a generally oval cross section with a flat facedisposed outwardly toward the circuit package, the fins having alignedopenings that are complementary with an outside size and shape of theheat pipe tube, for structurally attaching the fins and the heat pipetube wherein the heat pipe tube extends through said aligned openingsalong an edge of each of said fins, the openings forming at least onechannel along a side of the stack of fins; and, a clamping fixtureaffixed to at least one of the fins and the heat pipe tube, the mountingfixture being operable to hold the heat sink such that the heat pipetube is urged against the flat surface of the circuit package; whereinsaid at least one heat pipe tube has a flattened side facing outwardlyof the channel and the heat pipe tube has a shape with a relativelywider part disposed below an outer surface of the channel, and, whereinthe channel has a relatively narrower width at a point outwardly in thechannel from said relatively wider part, thereby capturing the heat pipetube and the fins to one another by the shape of the heat pipe tube andthe channel; wherein the heat pipe tube forms a U-shape with a flatbottom section of the U-shape with the flat face along a bottom of theflat bottom section, and wherein the clamping fixture is arranged toclamp over the bottom section to hold the flat face thereof against thecircuit package.